1. Field of the Invention
The present invention relates to an exposure apparatus for manufacturing devices such as semiconductor devices, liquid crystal display devices, or thin-film magnetic head by means of the lithography process. Also, the present invention relates to a method for manufacturing an exposure apparatus, and a method for manufacturing a device using an exposure apparatus.
2. Description of the Related Art
A conventional exposure apparatus is generally used for manufacturing semiconductor devices, liquid crystal display devices, or thin-film magnetic heads. This is a projection exposure apparatus which projects a predetermined pattern formed on a mask as a projection master onto a photosensitive substrate through a projection optical system. There are three types of conventional projection optical systems. A refraction type projection optical system comprises a refraction optical element having the optical property of transmitting an exposure light such as a lens. A reflection type projection optical system comprises a reflection optical element having an optical property of reflecting an exposure light such as a mirror. A conventional reflection and refraction type projection optical system comprises both reflection and refraction optical elements.
In order to manufacture highly integrated semiconductor devices the wave length of the exposure light has been shifted from the g-line toward the i-line, until the KrF excimer laser light had a wave length of 248 nm. Recently, an exposure light having a wave length of 193 nm can be produced by an ArF excimer laser. In the future, the more highly integrated semiconductor devices will be developed, the higher the resolution of a projection optical system in an exposure apparatus is required. A resolution of a projection optical system is represented by the formula below: EQU (resolution)=k*.lambda./NA,
where k denotes the k factor which is a positive constant, k&lt;1, which varies with the properties of the resist, .lambda. denotes the wave length of an exposure light, NA denotes a numerical aperture of a projection optical system.
As it is obvious from the above mentioned formula, reducing the wavelength .lambda. is a very efficient technique for increasing the resolution of a projection optical system. As a result, an exposure apparatus using a soft X-ray having a wave length of 5-15 nm (Extreme Ultra Violet radiation, or EUV radiation) as an exposure light has been developed recently. This exposure apparatus using EUV radiation is very prominent at the moment as a potential example of the technology of an exposure apparatus of the future.
The U.S. Pat. No. 5,917,879 discloses a projection optical system for an exposure apparatus using an EUV radiation.
In a projection optical system of an exposure apparatus using EUV radiation, a refraction optical device such as a lens cannot be used because no hyaline material can transmit EUV radiation. Moreover, the number of reflection optical elements must be minimized because reflection optical elements such as mirrors are extremely inefficient in their reflectivity, reflecting only about 65% of light. For example, a projection optical system disclosed in the U.S. Pat. No. 5,917,879 has four mirrors.
In the case of actual manufacture of a projection system, there are manufacturing errors of each optical member constituting a projection optical system (a refraction optical element, a reflection optical element), and structural errors. Therefore the required image resolution properties according to design rules of the future generations cannot be achieved without adjustments. The manufacturing errors of each optical member must be reduced to a negligible value to satisfy the required image properties.
When the size of an optical member is small, it is difficult to adjust the position of each optical member of a projection system after assembly in accordance with the measured image property. This is because the degree of freedom for adjustment is small.